Dilation catheter

ABSTRACT

A dilatation catheter having an outer tubular balloon portion with length-wise circumferential crimps having at either end transition portions with longitudinal crimps across the axis and an inner catheter is provided. The distal transition portion is fastened to the distal end of the inner catheter tube which extends beyond the distal end of the outer tube and the balloon portion while the proximal transition portion is connected to the distal end of the outer catheter tube. The balloon portion expands readily to a predetermined diameter while undergoing little change in length with an extension of the transition portions so that relative movement of the inner and outer catheter tubing is not required. Accordingly, minimum shear forces occur at the interface of the expanded balloon surface and the interior vessel wall.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of pending application Ser.No. 07/239,081, filed on Aug. 31, 1988, now U.S. Pat. No. 4,896,669.

BACKGROUND OF INVENTION

This invention relates to catheters and more particularly to dilatationcatheters which have an inflatable balloon portion which will not bedisplaced axially when inflated in a blood vessel to increase thepatency thereof.

It is a well known medical practice to use balloon catheters forenlarging the luminal diameter of a blood vessel, for example, at apoint of stenosis such as is produced by an accumulation of plaque. Inone procedure, known as percutaneous transluminal coronary angioplasty,the patent is viewed on an x-ray imaging screen while a flexible guidewire is first introduced through the skin into a coronary artery of apatient, and is so manipulated as to travel therein and penetrate thelumen of an occluded portion of the artery. A guide catheter is then fedalong the guide wire to a point in the artery which is just proximal ofthe occlusion. Finally, the dilatation catheter is sent along the guidewire, within the guide catheter, and into the artery of the patient toposition the balloon portion of the catheter in the occluded portion ofthe artery.

One such dilatation catheter has a flexible shaft which includes aninner tube, or cannula, which can pass freely along the guide wire and aflexible outer tube which surrounds the inner tube and has an innerdiameter which is somewhat larger than the outer diameter of the innertube. A flexible balloon portion at the distal end of the outer shaft issealed to the distal end of the inner tube. The balloon portion iscapable of expansion when fluid under pressure is directed into thespace between the outer tube or the shaft and the inner tube whereas theouter tube of the shaft is relatively more rigid and is not capable ofsuch expansion.

When the balloon portion of the catheter has been correctly positionedas seen on the x-ray imaging screen, a radiopaque, fluid contrast mediumis introduced under pressure into the space between the inner and theouter tubes to expand the balloon portion which presses against theoccluded matter on the inside of the artery. The expansion of theballoon must be carefully controlled to prevent possible over-expansionand over-stressing of the wall of the catheter which might cause it torupture, while putting sufficient force on the blood vessel toaccomplish the objectives of the procedure. When the desired enlargementof the occluded portion of the artery is completed, the pressure on thefluid inside the catheter is relieved, the balloon shrinks, and thecatheter is then removed.

In one catheter of the above type, the proximal end of the catheter isfitted to a mount which receives the proximal ends of the inner tube andof the shaft tube and seals them in spaced-apart relationship, whileproviding a passageway for supplying fluid under pressure to the spacetherebetween. When the catheter is pressurized, the inner tube shiftsits position to accommodate the decrease in the length of the balloonwhich occurs when the balloon expands. Upon release of pressure in thecatheter, the inner tube is returned to its original distal position sothat he movement of the inner tube aids in reducing the diameter of theballoon to approximately its original diameter, easing removal of thecatheter from the blood vessel.

Some of the known catheters of this type exhibit axial shrinkage of theballoon portion during inflation. In some prior art catheters,non-uniform axial shrinkage of the balloon during inflation results inundesirable curving of the distal portion of the balloon.

Accordingly, there is a need for a balloon catheter in which theexternal surface of the balloon portion does not rotate or changedimensions longitudinally during inflation and which, at the same time,does not experience significant axial displacement during inflation.Concomitant with the foregoing is a need for dimensional stability ofthe inflated balloon so that there is very little further expansion andstretch after the balloon reaches the desired inflated dimensions. Inthis way, overexpansion of the balloon and consequent damage to thevessel wall is minimized if the specified pressure is exceeded bymistake. The balloon which meets the foregoing needs should also becapable of rapid deflation and of subsequent complete recovery oforiginal dimensions so as to allow easy and prompt retrieval when theprocedure has been completed.

SUMMARY OF THE INVENTION

Generally speaking, in accordance with the invention, the foregoingrequirements are met by a catheter having an expandable balloon portionformed with length-wise circumferential pleat-like crimps which providea high degree of circumferential compliance up to a predetermined limitof expansion, e.g., the point at which the pleats are completelyunfolded. The distal and proximal connecting portions are crimped intolongitudinal pleat-like folds across the axis and provide aprecalculated degree of compliance in the axial direction of the shaft.

When fluid under pressure is supplied to the catheter via a spacebetween an inner and outer tubing, the balloon portion expands radially,but has little change in longitudinal dimension. Such little shorteningas occurs at the two ends of the balloon is accommodated by expansion ofthe connecting portions with substantially no change in radialdimension. The walls of the expanding balloon portion and of theconnecting portions are made of a fabric or thin high strength filmsubstrate which has been crimped and is treated with an elastomericmaterial. The elastomeric material resists penetration by thepressurizing fluid without interfering with the desired expansion of theballoon. The fabric substrate may be coated or impregnated withelastomer or an inner and outer sleeve of the elastomer may be placedabout the fabric substrate. When a film substrate is used elastomer isprovided on the outer surface of the crimped film, by coating the filmor placing an outer sleeve of elastomer about the crimped film. Theelastomer provides elasticity to the walls of the balloon and theconnecting portions to facilitate rapid deflation and subsequentcomplete recovery of original dimensions. In addition, the elastomerprovides a smooth outer surface for the balloon portion and theconnecting portions in the inflated as well as deflated state.

Accordingly, it is an object of the invention to provide an improveddilatation catheter.

It is another object of the invention to provide a balloon catheter inwhich expansion of the balloon does not result in longitudinal change ofballoon position within a blood vessel during a medical procedure.

A further object of the invention is to provide a balloon catheter whichdoes not curl as a result of inflation.

Still another object of the invention is to eliminate the undesirableeffects of longitudinal motion of a balloon catheter on the lumen of ablood vessel during inflation.

Still a further object of the invention is to provide a catheter havinga balloon portion with improved dimensional stability when inflated.

Yet another object of the invention is to provide a catheter having aballoon portion which will return to its original dimension rapidly upondeflation.

Yet a further object of the invention is to provide a balloon catheterwhich does not provide surface rotation upon inflation of the balloonportion.

Yet another object of the invention is to provide a balloon catheterwhich has a smooth outer surface for the balloon portion and thetransition portions in the uninflated as well as inflated state.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The invention accordingly, comprises an article of manufacturepossessing the features, properties, and the relation of elements whichwill be exemplified in the article hereinafter described, and the scopeof the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference is had to thefollowing description taken in connection with the accompanyingdrawings, in which:

FIG. 1 is a plan view of a balloon catheter fabricated according to theteachings of the invention, showing an attachment for supplyinginflating fluid under pressure;

FIG. 2a is a plan view of the balloon and transition portions showingthe balloon in an uninflated condition;

FIG. 2b is a plan view of the catheter of FIG. 2a wherein the transitionportions of the catheter are sewn to the balloon portion shown in aninflated condition;

FIG. 2c is a plan view of the catheter of FIG. 2a wherein the transitionportions are integrally formed with the balloon portion shown in aninflated condition;

FIG. 3 is a cross-sectional view along line 3--3 of FIG. 2a showing thecentral portion of the balloon with a fabric substrate in an uninflatedcondition;

FIG. 4 is a cross-sectional view along line 4--4 of FIG. 2b, showing theballoon portion of FIG. 3 in an inflated condition;

FIG. 5a is a cross-sectional view along line 5a--5a of FIG. 2a showingdetail of the distal balloon connection for a balloon having a fabricsubstrate in an uninflated condition;

FIG. 5b is a cross-sectional view along line 5b--5b of FIG. 2b showingdetail of the proximal balloon connection for a balloon having a fabricsubstrate;

FIG. 5c is a cross-sectional view along line 5c--5c of FIG. 2c showingdetail of the proximal balloon connection for a balloon having a fabricsubstrate;

FIG. 6 is a cross-sectional view of the proximal portion of the cathetershaft, showing the catheter fitting;

FIG. 7 is a cross-sectional view illustrating a portion of analternative construction of the catheter in an inflated condition;

FIGS. 8a-8b is a cross-sectional view along line 3--3 of FIG. 2a showingthe central portion of the balloon with a film substrate in anuninflated condition;

FIG. 9 is a cross-sectional view along line 4--4 of FIG. 2b, showing theballoon portion of FIG. 8 in an inflated condition;

FIG. 10a is a cross-sectional view along line 5a--5a of FIG. 2a showingdetail of the distal balloon connection for a balloon having a fabricsubstrate in an uninflated condition;

FIG. 10b is a cross-sectional view along line 5b--5b of FIG. 2b showingdetail of the proximal balloon connection for a balloon having a filmsubstrate;

FIG. 10c is a cross-sectional view along line 5c--5c of FIG. 2c showingdetail of the proximal balloon connection for a balloon having a filmsubstrate;

FIGS. 11aa--11e are schematic representations of crimped structuresuseful in fabricating balloon portions in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a catheter, generally designated 2 and having a distal tip6, with a guide wire 4 positioned in an inner passageway 3 of catheter2. Catheter 2 has a balloon portion 8 formed in a portion oflongitudinal shaft 10. As catheter 2 is inserted percutaneously in apatient, tip 6 first passes along guide wire 4, being followed byballoon portion 8 and as much of catheter shaft 10 as is necessary forballoon portion 8 to reach the desired region in the artery.

A proximal catheter fitting 12 remains external of the patient and isattached to a pressure tube 16 into which fluid can be forced by meansof a syringe 18 or other inflation device via a connecting tee 14.Pressure in the fluid can be monitored by means of a gauge 20 which isconnected to pressure tube 16 by means of a second connecting tee 22. Aguiding catheter which is also conventionally used in placing theballoon catheter in position in the blood vessel is not illustrated.

Reference is now made to FIGS. 2a, 2b and 2c for a general descriptionof the balloon region of catheter 2. FIGS. 2a is a plan view showingcatheter balloon 8 in an uninflated condition and FIGS. 2b and 2c showballoon 8 in an inflated condition. The distal end of catheter 2includes a tapered or conical distal tip 6 which may be made of plastic,a distal connecting portion 24, balloon portion 8, a proximal connectingportion 26 and an outer shaft tube 28. As detailed in FIG. 5a, tip 6 isformed with a tapered, angular ring within which the distal end of innercatheter tube 30 is sealed. Distal connecting portion 24 and proximalconnecting portion 26 are of the same pleated construction. In FIG. 2b adistal connecting portion 24a and a proximal connecting portion 26a aresewn to balloon portion 8a at stitching 29 and are capable of yieldinglongitudinally, as detailed in FIGS. 2b and 5b, while substantiallymaintaining the same outer diameter. In FIG. 2 c, transition portion 26bis shown as formed integrally with balloon portion 8b and expands in aradial direction at the connections with balloon portion 8b.

In order to provide for diametric expansion from the uninflatedcondition of FIG. 2a to the inflated condition of FIG. 2b, substrate 7of balloon portion 8 is pleated in the length-wise direction so as toprovide a low value of circumferential stiffness until a specific radiusis obtained, and to have an abrupt rise in circumferential stiffnessthereafter. Substrate 7 is treated with an elastomeric material 9, suchas polyurethane or other biologically acceptable elastomers to coat orimpregnate substrate 7. Alternatively, the elastomer may be in the formof inner and outer sleeves 9a and 9b as shown in FIG. 7. In addition,the wall of balloon portion 8 has a high stiffness in the axialdirection, so that there is little significant change in length alongmost of the length of balloon portion 8 when the balloon is inflated.These objectives are met by crimping the wall of the substrate ofballoon portion 8 to provide longitudinally stiff elements which yieldcircumferentially until a predetermined diameter is reached.

As can be seen by comparing the uninflated and the inflated balloons ofFIGS. 3 and 4, respectively, the crimped fabric substrate of balloonportion 8 results in its compact stowage around inner catheter tube 30.The uninflated balloon portion 8 has an outer diameter which is the sameas that of catheter tip 6 and of shaft tube 28, facilitating movement ofcatheter 2 within the artery of a patient. When inflated, the flatteningout of the accordion-pleat-like crimps in the wall of balloon portion 8(FIGS. 4 and 5b) limits further expansion thereof. The pleatedstructures are readily fabricated, for example, by crimping a tube oftextile fabric in the circumferential or the longitudinal direction,respectively and coating with elastomer.

Even though the high axial stiffness of balloon portion 8 will preventsubstantial changes in the active length during inflation, some changein overall length is unavoidable in the regions of attachment of theballoon portion to the catheter tip and to the distal end of the shafttube. To avoid the need for a compensating retraction of catheter tip 6,extendable connection portions 24 and 26 are provided at each end ofballoon portion 8. These portions extend axially when the balloon isinflate offsetting any retraction of the ends of balloon portion 8 sothat tip 6, balloon portion 8, and outer tubing 28 of catheter 2 remainstationary while the balloon is being inflated.

As depicted in FIGS. 5 and 6 for a fabric substrate and FIG. 10 for afilm substrate, connecting portions 24 and 26 are both constructed inthe form of cylinders which, after longitudinal crimping and coating,have an outer diameter which corresponds to that of shaft tube 28. Aswith the wall of balloon portion 8, the wall of each connecting portionis formed of a coated crimped fabric; but these structures resist radialexpansion while yielding longitudinally. The distal ends of connectingportions 24 and 26 are respectively bonded to the proximal wall ofcatheter tip 6 and are fixed to or integrally formed with the proximalend of balloon portion 8 while the proximal ends of the connectingportions are respectively fixed to or integrally formed with the distalend of balloon portion 8 and bonded to the distal end of outer cathetertubing 28, respectively.

FIG. 6 depicts, in partial cross-section, the proximal fitting 12 whichis used with catheter 2. Fitting 12 includes a solid block 29 having anaxial opening in which the proximal end of inner catheter tube 30 isseated. A passageway 34 surrounds inner tube 30, and communicates withpassageway 36 within outer catheter tube 28. Communicating radially withpassageway 34 is a fluid supply passageway 35 by means of which fluidunder pressure is fed into catheter 2. A conical aperture 37communicates axially with inner catheter passageway 3 through whichguide wire 4 is threaded.

In use, balloon portion 8 of catheter 2 is inflated by forcing fluidinto catheter 2 via tube 16 (FIG. 1). The fluid flows from tube 16 intoconnecting tee 14 of catheter fitting 12 (FIG. 6) where it passes intoan annular space 34 around the proximal end of inner catheter tube 30.From annular space 34, the fluid flows into an annular space 36 betweeninner tube 30 and outer tube 28, whence it flows past a radio-opaquemarker band 38 (FIG. 5b), through proximal connecting portion 26 andinto balloon portion 8, and finally into distal connecting portion 24.When balloon portion 8 expands under pressure of the fluid, it does sountil further expansion in diameter is limited by the flattening ofpleats of fabric substrate 7 into a substantially cylindrical balloonwall. At the same time, elongation of connecting portions 24 and 26offsets any small longitudinal shortening of balloon portion 8. When theangioplasty procedure has been completed, fluid is withdrawn fromcatheter 2 by reversing the action of syringe 18 and balloon portion 8and connecting portions 24 and 26 readily resume their originalconfigurations.

In an alternative form of construction shown in FIG. 7, the distalconnecting portion (not shown), a proximal connecting portion 40, and aballoon portion 8c are fabricated as before, being integrally formed,bonded or sewn together. However, the proximal end of proximalconnecting portion 40 is joined at 44 to the distal end of a long tube46 of a Dacron fabric of appropriate inner and outer diameter. Fabrictube 46 is threaded into an equally long outer tubing 48 of Teflon/FEPof appropriate diameter and bonded thereto with the connecting portionsand balloon portion 8c extending forward thereof. The outer surfaces ofthe connecting portions and balloon portions of the catheter prepared inaccordance with this embodiment are dip-coated with polyurethane 50 sothat the total outer diameters of these components, when the balloonportion is uninflated, matches that of the shaft section 48. After innercatheter tube 30, of appropriate diameter, has been passed into theforegoing assembly, the distal end of the inner tube is bonded, as wastube 30 in the first embodiment, to the distal end of the distalconnecting portion (not shown).

In a further alternative embodiment illustrated in FIGS. 8-10, thetextile component of a balloon is replaced by a thin high-strength film81. An expandable balloon portion 82 of the catheter is formed bycrimping and heat-setting film 81 to produce lengthwise circumferentialpleat-like crimps 82 which provide a high degree of circumferentialcompliance up to a pre-determined limit of expansion, e.g., the point atwhich the crimps are completely straightened. A tubular elastomericsleeve 83 is fitted over the length of balloon portion 80. Elastomericsleeve 83 facilitates rapid deflation of balloon 80 upon release ofinternal pressure and subsequent complete recovery of originaldimensions. Alternatively, the external surface of the crimped wall ofballoon portion 80 can be coated with an elastomer coating 84 as shownin FIG. 8b to produce a smooth outer surface. FIG. 9 illustrates incross-section balloon 80 in an expanded condition and pleats 82 in astraightened condition.

Film 81 is preferably a heat-settable, biaxially oriented, high-strengthpolymeric film such as polyester. The plain flat film can first becrimped with a multitude of length-wise pleat-like crimps, preferablytriangular in cross-section as shown in FIG. 11a. The crimped film canbe cut to the appropriate length corresponding to the length of theballoon portion to be formed. The tubular balloon portion can then beformed from the crimped film by bonding the free edges togetherlength-wise. The tubular elastomeric sleeve can be conveniently producedby extrusion of a biocompatible polyurethane.

Since the crimped wall of balloon portion 80 is fluid-impermeable in thecase of a film substrate, this balloon construction requires only oneouter tubular elastomeric component or sleeve around the crimped wall,or an outer surface coating. The need for elastomeric impregnation ofthe textile structure and/or the need for the inner tubular elastomericsleeve as discussed in the earlier embodiment is eliminated.

FIG. 10a illustrates the anchoring of balloon portion 80 to distal tip 6as in FIG. 5a . FIG. 10b illustrates a connection 86 of balloon portion80 to the distal end of catheter outer shaft tube 28 shown in anexpanded condition. Balloon 80 is formed integrally with transitionportion 26b in FIG. 10c.

FIG. 11a is a view in cross-section of a "triangular" crimp geometrywhich may be employed in forming the accordion-like walls of balloonportions 8 and 80 and of expansion sections 24, 26 or 40; FIGS. 11a-11eare schematic representations showing various geometric forms of thecrimps which may be employed in the structures prepared in accordancewith the invention. In FIG. 11b the crimps are formed into parabolas p'and p" of differing shape. FIG. 11d is the limiting case for thepreceding embodiments in which the crimps are of substantiallyrectangular cross-section. FIG. 11e illustrates a folded structure inwhich the crimping forms a wall of a series of sequentially invertedfrustums of triangles. The foregoing geometries lend themselves readilyto mathematical analysis for comparison of relative structuraladvantage.

It will be seen that, when using the straight-sided, triangular crimp ofFIG. 11a, the radial depth H is proportional to the pitch distance P_(o)when crimp angle φ_(o) is kept constant so that the small pitchdistances desirably reduce the radial depth H of a crimp section,providing a more compact structure while still providing the same degreeof expansion. When the fabric or film thickness is taken into account indesigning such a triangular configuration, the thickness as well as thesubstrate type, e.g. the type of yarn, weave, etc., or the film typemust be chosen to meet the following criteria: ##EQU1## where σ.sub.Θand σ_(z) respectively are the circumferential tensile strength and theaxial tensile strength of the substrate, ψ is the desired burstpressure, D1 is the inner diameter of the inflated balloon, D2 is theouter diameter of the inflated balloon, and t is the thickness of thesubstrate used for balloon construction. The right-hand sides of theequations represent the stresses in the wall of the inflated balloon inthe circumferential and the axial direction, respectively.

Further, given a minimum wall thickness (t) of the inflated ballooncalculated by equations (1) and (2), the unstretched crimp angle φ_(o)for a given number of crimps per unit length (n) and a given undeformedcrimp height (H) can be determined by trial-and-error calculation fromthe equation: ##EQU2## which is derived from the geometry of thestructure.

The ratio λ of fully extended crimp length to initial (uninflated) crimplength is related to φ_(o) by the equation:

    λ=(cos φ.sub.o).sup.-1                          (4)

Illustrative calculations are presented below.

For a number of crimps per mm n=2.25, a height H of 0.9 mm, and athickness t of 0.2 mm, trial-and-error solution or equation (3) andequation (4) yield φ_(o) ˜65° and λ=2.37. Increasing the value of n to5.0, while keeping φ_(o) 65° and t=0.2 mm, yields a height H of 0.687mm, which is 24% less than that of the first calculated example, thusreducing the profile (outside diameter) of the uninflated balloon.

The uninflated outside diameter OD of the balloon, given a predeterminedinside diameter ID and an uninflated crimp height of H is determined asfollows:

    OD=ID+2H

Thus, for an uninflated ID of 0.5 mm and the above calculated H=0.687,the uninflated OD of the balloon is 1.87 mm plus the thickness of thepolyurethane coating and the inflated OD is 2.37×(0.5+0.687), or 2.813mm plus the thickness of the polyurethane coating.

If a substrate thickness of 0.1 mm provides adequate burst strength,then, given H=0.687 mm, n=5, and t=0.1 mm, trial-and-error solution ofequation (3) yields values of φ_(o) 73.4° and λ=3.5. For the sameuninflated balloon OD, the inflated OD now is 4.155 mm plus thethickness of the polyurethane coating. Although the above calculation isshown for triangular crimps, the other crimp geometries will yield muchhigh λ values:

    (   >   >  > > ).

By similar calculations, it can b shown that for identical crimp heightsand pitches, the parabolic (FIG. 11b) crimp geometry will yield higherexpansion in diameter than the triangular crimp geometry, while the"frustum of triangle" crimp geometry (FIG. 11d) will yield a stillhigher diameter. On the other hand, for the same expandability and thesame crimp pitch, the parabolic crimp geometry will require less crimpheight than the triangular crimp geometry and the "frustum of triangle"crimp geometry will require still less, providing lower uninflatedprofiles for the balloon portion of the catheter for a given uninflatedballoon inside diameter.

In the alternative, for a given uninflated balloon outside diameter,reduced crimp height results in increased inside diameter of theuninflated balloon, allowing use of a larger diameter inner tube andproviding improved fidelity in distal pressure wave monitoring. Thefrustum of triangle structure of FIG. 11e yields the highest ratio offully inflated balloon diameter to uninflated balloon diameter for givenvalue of crimp height and crimp pitch. At the same time, the frustum oftriangle crimp geometry results in the smallest required crimp heightfor the desired expandability and the given crimp pitch, yielding thelowest uninflated profile for the balloon for a given uninflated ballooninner diameter. Where the catheter is also to be used for distalpressure wave monitoring, the smaller frustum of triangle crimp geometryfor a given uninflated balloon outer diameter also permits increasingthe inner diameter of the uninflated balloon, thus allowing use of aninner tube having larger inner and outer diameters, thereby improvingthe fidelity of pressure wave transmission.

The balloon portion and connecting portions of the balloon catheterconstructed in accordance with the invention can be fabricated usingsuitable biologically compatible materials. The fabric substrate can beknitted or woven polyester or a polyester film which is appropriatelycrimped and then coated with an elastomeric material. The elastomer mustprovide surface smoothness and be non-thrombogenic. The adjoining fabricor film sections can be sewn together or formed integrally and the freeends of the expansion portions appropriately bonded to the rear surfaceof the catheter tip and the distal surface of the catheter shaft tube asdescribed above. Other structures can, of course, be employed.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in the above article without departingfrom the spirit and scope of the invention, it is intended that allmatter contained in the above description and shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

What is claimed:
 1. A dilatation catheter, comprising:a length of ashaft of flexible material having a longitudinal axis; an inner flexiblemember coaxially disposed in the shaft and having a distal portionprojecting therefrom; a balloon portion formed at the distal end of theflexible shaft, the balloon portion formed with radial crimps runninglength-wise about the circumference thereof and being capable ofexpanding to a predetermined diameter when subjected to internalpressure to provide a balloon, the balloon portion fixed to the distalend of the flexible shaft and the distal end of the inner flexiblemember; and a transition portion at at least one end of the balloonportion surrounding the inner flexible member for coupling the balloonportion to one of the inner distal ends of the flexible member and thodistal portion of the flexible shaft, the transition portion beingcapable of longitudinal extension in response to a minor longitudinalcontraction at the two ends of the balloon portion when the balloonportion is inflated.
 2. The dilatation catheter of claim 1, in which thecrimps have a triangular cross-section.
 3. The dilatation catheter ofclaim 1, in which the crimps have a curvilinear cross-section.
 4. Thedilatation catheter of claim 1, in which the crimps have a cross-sectionin the form of a frustum of triangle.
 5. The dilatation catheter ofclaim 1, in which the film is polyester.
 6. The dilatation catheter ofclaim 5, in which the polyester is coated with polyurethane.
 7. Thedilatation catheter of claim 1, further including a radio-opaque memberto aid in positioning the catheter during use.
 8. The dilatationcatheter of claim 1, wherein the film substrate is a dacron film and theelastomeric material is a polyurethane.
 9. The dilatation catheter ofclaim 8, wherein the elastomer is an outer sleeve disposed about thecrimped film.
 10. A dilatation catheter, comprising:a length of atubular shaft of flexible material having a longitudinal axis; an innertubular flexible member coaxially disposed in the shaft and having adistal portion projecting therefrom; a balloon portion formed at thedistal end of the flexible shaft, the balloon portion formed with aplurality of circumferential crimps running length-wise being capable ofexpanding radially to a predetermined diameter with minor axial movementwhen subjected to internal pressure to provide a balloon, the balloonportion fixed to the distal end of the tubular flexible shaft and thedistal end of the inner tubular flexible member; and a transitionportion end of the balloon portion surrounding the inner flexible memberformed with a plurality of longitudinal crimps across the length of thecatheter for coupling the balloon portion to the distal end of the innertubular flexible member and the distal portion of the tubular flexibleshaft, the transition portion being capable of longitudinal extension inresponse to a minor longitudinal contraction at the two ends of theballoon portion to reduce the axial movement when the balloon portion isinflated; and the balloon portion and the transition portions are formedfrom a flexible thin film substrate and an elastomer to provide a smoothouter surface.